Catalytic hydrogenation over rhenium-containing catalysts supported on activated carbon

ABSTRACT

In a process for preparing alcohols by catalytic hydrogenation of carbonyl compounds over a catalyst comprising rhenium on activated carbon, the catalyst used comprises rhenium (calculated as metal) in a weight ratio to the activated carbon of from 0.0001 to 0.5, platinum (calculated as metal) in a weight ratio to the activated carbon of from 0.0001 to 0.5 and, if appropriate, at least one further metal selected from among Zn, Cu, Ag, Au, Ni, Fe, Ru, Mn, Cr, Mo, W and V in a weight ratio to the activated carbon of from 0 to 0.25, and the activated carbon has been nonoxidatively pretreated. It is also possible to prepare ethers and lactones if the hydrogen pressure is not more than 25 bar. In this case, the activated carbon in the catalyst may also have been nonoxidatively pretreated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional application of application Ser. No. 10/220,566,filed on Dec. Oct. 29, 2002, now U.S. Pat. No. 6,906,228, the entiredisclosure of which is herewith incorporated by reference, which is aU.S. national stage application under 35 U.S.C. §371, based onInternational application No. PCT/EP01/02337, filed Mar. 1, 2001, theentire disclosure of which is herewith incor-porated by reference.

The present invention relates to a process for the hydrogenation ofcompounds containing carbonyl groups over Re-containing, sometimesnonoxidatively pretreated catalysts supported on activated carbon forpreparing alcohols while avoiding the formation of ethers, or forpreparing ethers and lactones, with the preparation of the desiredproduct being able to be controlled selectively.

The industrial preparation of alcohols frequently starts out fromstarting materials containing carbonyl groups, for example aldehydes,ketones, carboxylic acids, carboxylic anhydrides and esters, which arehydrogenated by means of hydrogen. The preparation of ethers andlactones frequently starts out from carboxylic acids, esters oranhydrides thereof, lactones or mixtures thereof.

In the recent past, particularly active catalysts using oxidativelypretreated activated carbon supports which have been oxidativelypretreated have been found. EP-A-0 848 991 describes a palladium-,silver-, rhenium- and iron-containing catalyst which, for example, canhydrogenate maleic acid or its esters to give butanediol. In thehydrogenation of maleic acid at from 100 to 162° C., a selectivity tobutanediol of 89.5% is achieved. However, the formation of 5.6% oftetrahydrofuran (THF) as ether by-product detracts from the success ofthe hydrogenation. In addition, 4% of n-butanol is formed as furtherby-product.

U.S. Pat. No. 5,698,749 describes catalysts comprising an element ofgroup VIII and additionally at least rhenium, tungsten or molybdenum onan oxidatively pretreated carbon support. In particular, Pd/Re/C orPd/Re/Ag/C catalysts are described. Once again, THF is formed inaddition to butanediol when using these catalysts in the hydrogenationof aqueous maleic acid. Here, butanediol is obtained in a selectivity ofup to 92.8%, but THF is still formed in an amount of 1.6% and thefurther by-product n-butyl is formed in an amount of 4.6%.

The tendency of the hydrogenation metals rhenium or platinum to form THFand thus an ether in the hydrogenation of maleic acid derivatives isknown (cf., for example, A. F. Timofeev et al., Prikl. Khim. (Leningrad)1981, 54(2), 335–8, Chemical Abstracts 95: 80602×. The same effect isalso described in GB-A-1 551 741 for the use of supported Pd/Re, Pt/Reor Pt/Pd/Re catalysts.

H. S. Broadbent et al., in J. Org. Chem. 24, 1847–1854 (1959) describethe hydrogenation of succinic acid over unsupported metallic Re, inwhich considerable amounts of THF are formed.

The avoidance of ethers as by-product is, however, desirable inindustrial hydrogenation processes for preparing alcohols since theirformation adversely affects the economics of the process. Furthermore,the ethers are sometimes difficult to separate from the desired product.The ethers also result in considerable disposal costs. THF, for example,is difficult to degrade biologically and must therefore no longer beintroduced, even in small amounts, into a water treatment plant.

U.S. Pat. No. 5,478,952 relates to the hydrogenation of maleic acid overan Ru/Re activated carbon catalyst to form THF and gamma-butyrolactoneas main products.

EP-A-0 276 012 relates to the hydrogenation of maleic acid togamma-butyrolactone and butanediol over Pd/Re/TiO₂ catalysts.

Owing to the high corrosivity of acid solutions at high temperatures andpressures, it is desirable to carry out the hydrogenation at lowtemperatures.

It is an object of the present invention to provide rhenium catalysts bymeans of which carbonyl compounds can either be hydrogenated to alcoholswith high overall selectivity, without ethers being formed, or can behydrogenated selectively to ethers and lactones.

We have found that this object is achieved by a process for thecatalytic hydrogenation of carbonyl compounds over a catalyst comprisingrhenium on activated carbon, wherein the catalyst used comprises rhenium(calculated as metal) in a weight ratio to the activated carbon of from0.0001 to 0.5, platinum (calculated as metal) in a weight ratio to theactivated carbon of from 0.0001 to 0.5 and, if appropriate, at least onefurther metal selected from among Zn, Cu, Ag, Au, Ni, Fe, Ru, Mn, Cr,Mo, W and V in a weight ratio to the activated carbon of from 0 to 0.25,for preparing alcohols, in which case the activated carbon has beennonoxidatively pretreated, or for preparing ethers and lactones, inwhich case the starting substances are carboxylic acids, esters oranhydrides thereof, lactones or mixtures thereof, the hydrogenation iscarried out at a hydrogen pressure of not more than 25 bar and theactivated carbon may have been nonoxidatively pretreated.

It has been found that carbonyl compounds can be hydrogenatedcatalytically to give the corresponding alcohols without ether formationat low temperatures (preferably below 140° C.) when at least rhenium orrhenium/platinum on nonoxidatively pretreated carbon supports such asactivated carbon are used for the hydrogenation.

In the present context, the expression “without ether formation” meansthat any ether formed should make up not more than 0.5% of thehydrogenation products. The ether content is preferably below 0.2%,particularly preferably below 0.1%.

At low pressures, the preparation of ethers and lactones, generally inadmixture, is possible. The reaction can be controlled and directed atthe desired products by means of the hydrogen pressure, withpredominantly alcohols being formed at relatively high pressures andpredominantly ethers and lactones being formed at low pressures. In thisway, ethers can be formed as main products.

A nonoxidative treatment of the carbon support material with mineralacids or bases is advantageous compared to an oxidative treatment withHNO₃ or peroxides since an oxidative pretreatment of activated carbonwith H₂O₂ or peroxides represents an expensive pretreatment processwhich considerably increases the catalyst manufacturing costs. Theoxidative pretreatment with HNO₃ results in formation of nitrous gaseswhich have to be removed in complicated waste gas purification processes(DeNOX). A further disadvantage of oxidative pretreatment is thematerial loss of support material caused by the oxidative pretreatment.The carbon-containing support materials partly dissolve in the oxidizingagents and shaped bodies can even disintegrate completely if thetemperature is too high.

As activated carbon, commercially available activated carbons aregenerally suitable. Preference is given to using ones which containlittle chlorine and sulfur and whose proportion of micropores relativeto the proportion of mesopores and macropores is very low. Thenonoxidative treatment of the activated carbon can in the simplest casebe carried out by treatment with solvents such as water or alcohols. Thecarbon support can also be conditioned by nonoxidative treatment withmineral acids such as HCl, H₃PO₄, H₂SO₄, HBr or HF. Organic acids suchas formic acid or acetic acid can also be used for the pretreatment ofthe support material. Carbon supports which have been treated withsolutions of bases such as NH₄OH, NaOH or KOH likewise have a positiveeffect on the catalytic performance.

The treatment of the activated carbon with the nonoxidizing treatmentagent can be carried out before or during the application of theplatinum and rhenium components or further catalyst components.

In a further particular embodiment, use is made of catalysts in whichthe activated carbon support is firstly pretreated nonoxidatively and isthen pretreated oxidatively. In a further particular embodiment, use ismade of catalysts in which the activated carbon support is firstlypretreated oxidatively and is then pretreated nonoxidatively.

In a preferred nonoxidative pretreatment, the activated car on supportis stirred in the pretreatment agent at elevated temperature (50–90°C.). As pretreatment agents, it is possible to use either concentratedor dilute pretreatment agents (acids, alkalis). Preference is given tousing concentrated pretreatment agents (conc. HCl, conc. NaOH, halfstrength H₃PO₄). The treatment time is generally in the range from 1 to48 hours, preferably from 5 to 30 hours. After the treatment, the carbonsupport is freed of interfering ions by washing with water. Anafter-treatment in water at elevated temperature (for from 1 to 48hours, preferably from 5 to 30 hours) can follow.

When acidic pretreatment agents are used, a pH test (5 g of carbonsupport boiled in distilled H₂O for 20 minutes, solution filtered,allowed to cool under nitrogen, pH measured at 20° C.) indicates a moreacidic surface than in the case of the starting material, while the useof basic pretreatment agents results in a more basic surface.

As rhenium component, use is usually made of (NH₄)ReO₄, Re₂O₇, ReO₂,ReCl₃, ReCl₅, Re(CO)₅Cl, Re(CO)₅Br or Re₂(CO)₁₀, without this listingbeing intended to be exclusive. Preference is given to using Re₂O₇.

Apart from rhenium, platinum is also applied to the catalyst. Theplatinum can be applied as, for example, platinum powder, oxide,hydrated oxide, nitrate, platinum(II) or (IV) chloride,hexachloroplatinic(IV) acid, platinum(II) or (IV) bromide, platinum(II)iodide, cis- or trans-diammineplatinum(II) chloride, cis- ortrans-diammineplatinum(IV) chloride, diammineplatinum(II) nitrite,(ethylenediamine)platinum(II) chloride, tetrammineplatinum(II) chlorideor chloride hydrate, tetrammineplatinum(II) nitrate,(ethylenediamine)platinum(II) chloride,tetrakis(triphenylphosphine)platinum(0), cis- ortrans-bis(triethyl-phosphine)platinum(II) chloride, cis- ortrans-bis(triethylphosphine)platinum(II) oxalate,cis-bis(triphenylphosphine)platinum(II) chloride,bis(triphenylphosphine)-platinum(IV) oxide,(2,2′-6′,2″-terpyridine)platinum(II) chloride dihydrate,cis-bis(acetonitrile)platinum dichloride, cis-bis(benzonitrile)platinumdichloride, platinum(II) acetylacetonate,(1c,5c-cyclooctadiene)platinum(II) chloride or bromide, platinumnitrosyl nitrate, preferably as platinum oxide or nitrate, particularlypreferably as platinum nitrate, without this listing being intended tobe exclusive.

Rhenium (calculated as metal) can be applied in a weight ratio to theactivated carbon of from 0.0001 to 0.5, preferably from 0.001 to 0.2,particularly preferably from 0.01 to 0.15. The same ratios apply forplatinum. The weight ratio of rhenium to platinum (calculated as metals)is in the range from 0.01 to 100, preferably from 0.05 to 50,particularly preferably from 0.1 to 10.

Further elements can additionally be present on the catalyst. Exampleswhich may be mentioned are Zn, Cu, Ag, Au, Ni, Fe, Ru, Mn, Cr, Mo, W andV. These elements modify the catalyst essentially in respect of activityand selectivity (hydrogenolysis products), but are not absolutelynecessary. Their weight ratio to Re can be from 0 to 100, preferablyfrom 0.5 to 30, particularly preferably from 0.1 to 5.

The application of the active components Re and Pt can be carried out byimpregnation in one or more steps with an aqueous or alcoholic solutionor solution in other organic solvents of the respective salts,impregnation with a solution of an oxidic or metallic colloid of theactive components, equilibrium adsorption in one or more steps of thesalts dissolved in aqueous or alcoholic solution or equilibriumadsorption of dissolved metallic or oxidic colloid on the pretreatedactivated carbon. In these methods, the active components can be appliedto the activated carbon either simultaneously or in succession. A dryingstep for removal of the solvent is carried out between each of theindividual impregnation or equilibrium adsorption steps. The activecomponents are preferably applied by impregnation with an aqueous saltsolution or an aqueous oxidic colloid in one step.

To remove the solvent after the impregnation or equilibrium adsorptionstep, the impregnated catalyst is dried. The drying temperature is30–350° C., preferably 40–280° C., particularly preferably 50–150° C.

The catalysts are usually activated before use. This activation can beachieved by allowing a reducing gas atmosphere to act on the catalyst.Activation by means of hydrogen is preferably employed. The activationtemperature is usually 100–500° C., preferably 130–400° C., particularlypreferably 150–350° C. Alternative reduction methods are reduction ofthe metallic components by bringing the catalyst into contact with aliquid reducing agent such as hydrazine, formaldehyde or sodium formate.Here, the liquid reducing agents are usually brought into contact withthe catalyst at from 10 to 100° C., particularly preferably from 20 to80° C.

The hydrogenation for preparing alcohols is usually carried out at50–250° C., preferably 60–220° C., particularly preferably 70–190° C.,very particularly preferably 80–140° C. The hydrogenation is usuallycarried out at a reaction pressure in the range from 3 to 330 bar,preferably from 20 to 300 bar. The pressure of the hydrogenation in theliquid phase over a fixed bed is preferably above 150 bar, morepreferably 150–300 bar, in the gas phase over a fixed bed it ispreferably from 3 to 100 bar and in suspension it is preferably from 10to 90 bar.

Suitable starting materials for the hydrogenation for preparing alcoholsare carbonyl compounds in general, which may additionally contain C—Cdouble or triple bonds. Examples of aldehydes are propionaldehyde,butyraldehyde, croton-aldehyde, ethylhexanal, nonanal and glucose.Examples of carboxylic acids are succinic acid, fumaric acid, maleicacid, glutaric acid, adipic acid, hydroxycaproic acid, octanedioic acid,dodecanedioic acid, 2-cyclododecylpropionic acid and saturated orunsaturated fatty acids. Esters which may be mentioned are esters of theabovementioned acids, for example methyl, ethyl, propyl or butyl esters;lactones such as gamma-butyrolactone, delta-valerolactone orcaprolactone can also be used. Furthermore, it is possible to useanhydrides such as succinic anhydride or maleic anhydride. Preferredstarting materials are succinic acid, maleic acid, adipic acid,2-cyclododecylpropionic acid, succinic anhydride, maleic anhydride andesters of these acids and gamma-butyrolactone.

For the preparation of ethers and lactones, it has been found that, inparticular, C₄–C₅-dicarboxylic acids, -dicarboxylic esters and-dicarboxylic anhydrides can be hydrogenated catalytically to giveprimarily the corresponding cyclic ethers and lactones as furthercomponents of value at low hydrogen pressures (≦25 bar, preferably ≦20bar) when at least rhenium and platinum on carbon supports such asactivated carbon are used for the hydrogenation.

Only gamma-butyrolactone (GBL) has hitherto been obtained at similarlylow pressures. A further considerable disadvantage has hitherto been anincomplete acid conversion at such low pressures. These disadvantagesare now overcome.

The hydrogenation is preferably carried out at from 50 to 250° C.,preferably from 60 to 240° C., particularly preferably from 70 to 235°C.

The cyclic ethers and lactones obtained in the process of the presentinvention are used, for example, as solvents and intermediates. Atreatment of the carbon support material can also be carried out for thepreparation of ethers and lactones, but is not absolutely necessary.

Suitable starting materials for the hydrogenation for preparing ethersand lactones are carbonyl compounds in general, which may additionallycontain C—C double or triple bonds. Examples of carboxylic acids aresuccinic acid, fumaric acid, maleic acid, glutaric acid, adipic acid,hydroxycaproic acid. Suitable esters are esters of the abovementionedacids, for example the methyl, ethyl, propyl or butyl esters; it is alsopossible to use lactones, for example γ-butyrolactone, δ-valerolactoneor caprolactone. Anhydrides such as succinic anhydride or maleicanhydride can also be used. Preferred starting materials are succinicacid, maleic acid, adipic acid, succinic anhydride, maleic anhydride andthe esters of these acids and γ-butyrolactone. Particular preference isgiven to hydrogenating maleic acid, fumaric acid, succinic acid oresters or anhydrides thereof or gamma-butyrolactone to form THF andgamma-butyrolactone.

The compounds to be hydrogenated can be hydrogenated in bulk or insolution. Possible solvents are, for example, the hydrogenation productitself or substances which are inert under the reaction conditions, e.g.alcohols such as methanol, ethanol, propanol or butanol or ethers suchas THF or ethylene glycol ethers. A preferred solvent is water,particularly in the hydrogenation of carboxylic acids.

The hydrogenation can be carried out in the gas or liquid phase, in oneor more stages. In the liquid phase, both the suspension mode and thefixed-bed mode are possible. In the case of exothermic reactions, theheat can be removed by means of external coolants (e.g. shell-and-tubereactor). Evaporative cooling in the reactor is also possible,especially when the hydrogenation is carried out without productrecycle. In the case of product recycle, a cooler in the recycle streamis a possibility.

The alcohols obtained in the process of the present invention are used,for example, as solvents and intermediates. Diols such as butanediol areused as diol component in polyesters. 2-Cyclododecylpropan-1-ol is asought-after musk fragrance.

The process of the present invention is illustrated by the followingexamples. The contents of the individual components reported for thehydrogenation products have been determined by gas chromatography. Theyare, unless indicated otherwise, calculated on a solvent-free basis.

EXAMPLES Preparation of Alcohols Example 1 (Comparison)

20 g of activated carbon (Epibon Spezial®, from Lurgi) were oxidativelypretreated using 95% strength H₂SO₄, impregnated with 5 g of Re₂O₇ and15 g of platinum nitrate solution (=2.5 g of PtO₂) and dried. Thefurther procedure was as follows: for 30% strength maleic acid solution,a reaction temperature of about 155° C. and a total time of 78 hours,about 94% of butanediol and 5.26% of n-butanol, 0.31% of propanol, 0.3%of methanol and 0.3% of THF were found in the product.

Example 2 (Comparison)

Using a method analogous to Example 1, 20 g of activated carbon (BG 09®,from Jacobi) were oxidatively pretreated using 44% strength H₂SO₄,impregnated with 5 g of Re₂O₇ and 15 g of platinum nitrate solution(=2.5 g of PtO₂) and dried. The further procedure was as in Example 1.For 30% strength maleic acid solution, a reaction temperature of about141° C. and a total time of 78 hours, about 76.63% of butanediol and20.53% of n-butanol, 1.84% of propanol, 0.52% of methanol and 0.49% ofTHF were found in the product.

Example 3

Using a method analogous to Example 1, 20 g of activated carbon (BG 09®,from Jacobi) were nonoxidatively pretreated using 1 M NaOH, impregnatedwith 5 g of Re₂O₇ and 15 g of platinum nitrate solution (=2.5 g of PtO₂)and dried. The further procedure was as in Example 1. For 30% strengthmaleic acid solution, a reaction temperature of about 122° C. and atotal time of 78 hours, about 88.92% of butanediol and 10.77% ofn-butanol, 0.3% of propanol and no THF were found in the product.

Example 4

Using a method analogous to Example 1, 20 g of activated carbon (BG 09®,from Jacobi) were nonoxidatively pretreated using concentrated HCl,impregnated with 5 g of Re₂O₇ and 15 g of platinum nitrate solution(=2.5 g of PtO₂) and dried. The further procedure was as in Example 1.For 30% strength maleic acid solution, a reaction temperature of about114° C. and a total time of 78 hours, about 92.13% of butanediol and7.87% of n-butanol and no THF were found in the product.

Example 5

Using a method analogous to Example 1, 20 g of activated carbon (BG 09®,from Jacobi) were nonoxidatively pretreated using steam and subsequently5% strength HCl, impregnated with 5 g of Re₂O₇ and 15 g of platinumnitrate solution (=2.5 g of PtO₂) and dried. The further procedure wasas in Example 1. For 30% strength maleic acid solution, a reactiontemperature of about 131° C. and a total time of 78 hours, about 91.4%of butanediol and 8.26% of n-butanol, 0.32% of propanol and no THF werefound in the product.

Example 6

Using a method analogous to Example 1, 20 g of activated carbon (BG 09®from Jacobi) were nonoxidatively pretreated using 44% strength H₃PO₄,impregnated with 5 g of Re₂O₇ and 15 g of platinum nitrate solution(=2.5 g of PtO₂) and dried. The further procedure was as in Example 1.For 30% strength maleic acid solution, a reaction temperature of about107°C. and a total time of 78 hours, about 93.36% of butanediol and5.86% of n-butanol, 0.21% of methanol and no THF were found in theproduct.

Catalysts produced by nonoxidative treatment of the activated carbonwere able to hydrogenate maleic acid to the target product1,4-butanediol at a lower temperature than the known catalysts. Inaddition, the proportion of ether by-product could be greatly reduced.

Preparation of Ethers and Lactones Example 1

60 g of activated carbon (Epibon from Lurgi) were pretreated withphosphoric acid and dried at 120° C. 50 g of the carbon which had beenpretreated in this way were impregnated with 9.81 g of Pt(NO₃)₂ as anaqueous solution. The impregnated activated carbon was dried at 110° C.for 18 hours, subsequently reduced in a stream of nitrogen/hydrogen at300° C. and ambient pressure for 4 hours and passivated at roomtemperature in a stream of nitrogen/air. The passivated catalyst wassubsequently impregnated with 5 g of Re₂O₇ and dried at 110° C. for 18hours. The catalyst obtained in this way was activated in a stream ofnitrogen/hydrogen at 300° C. and ambient pressure for 4 hours andpassivated at room temperature in a stream of nitrogen/air. The reducedcatalyst contains 3% of Pt and 3% of Re. 25 ml of theactivated/passivated catalyst were subsequently placed in a reactorhaving a capacity of 25 ml.

The hydrogenation was carried out in the downflow mode, without productrecirculation. The reaction pressure was 20 bar and about 180 standard1/h of hydrogen were fed in. At a maleic acid concentration of 30%(water), an LHSV of 0.1 h⁻¹ and a reactor temperature of 235° C., thehydrogenation product comprised about 73.5% of THF, 1.3% of GBL, 0% ofBDO and 25.0% of alcohols (n-butanol+n-propanol) after a total of 3hours. The acid conversion was 95.3%. At an LHSV of 0.2 h⁻¹ butotherwise identical conditions, a hydrogenation product comprising about36.5% of THF, 42.7% of GBL, 0.90% of BDO and 19.8% of alcohols(n-butanol+n-propanol) was obtained after a time of 17.5 h. The acidconversion was 95.1%.

Example 2 (Reference)

60 g of activated carbon (Epibon from Lurgi) were pretreated withphosphoric acid and dried at 120° C. 50 g of the carbon which had beenpretreated in this way were impregnated with 2.5 g of PdCl₂ as anaqueous solution. The impregnated activated carbon was dried at 110° C.for 18 hours, subsequently reduced in a stream of nitrogen/hydrogen at300° C. and ambient pressure for 4 hours and passivated at roomtemperature in a stream of nitrogen/air. The passivated catalyst wassubsequently impregnated with 5 g of Re₂O₇ and dried at 100° C. for 18hours. The catalyst obtained in this way was activated in a stream ofnitrogen/hydrogen at 300° C. and ambient pressure for 4 hours andpassivated at room temperature in a stream of nitrogen/air. The reducedcatalyst contains 3% of Pd and 3% of Re. 25 ml of theactivated/passivated catalyst were subsequently placed in a reactorhaving a capacity of 25 ml.

The hydrogenation was carried out in the downflow mode, without productrecirculation. The reaction pressure was 20 bar and about 100 standard1/h of hydrogen were fed in. At a maleic acid concentration of 30%(water), an LHSV of 0.1 h⁻¹ and a reactor temperature of 235° C., thehydrogenation product comprised about 65.2% of THF, 11.9% of GBL, 0% ofBDO and 22.9% of alcohols (n-butanol+n-propanol) after a total of 3hours. The acid conversion was 98.5%.

When using Pt/Re catalysts on activated carbon support materials, maleicacid can be hydrogenated at low hydrogen pressures to give predominantlythe target product tetrahydrofuran and small proportions ofgamma-butyrolactone as further product of value with high acidconversions and higher selectivities than those obtained usingcomparable Pd/Re activated carbon catalysts.

1. A catalyst comprising rhenium and platinum on activated carbon havingfrom 0.0001 to 0.5 part by weight of rhenium (calculated as metal), from0.0001 to 0.5 part by weight of platinum (calculated as metal) and,optionally, from 0 to 0.25 part by weight of at least one further metalselected from among Zn, Cu, Ag, Au, Ni, Fe, Ru, Mn, Cr, Mo, W and V(calculated as metal) on 1 part by weight of nonoxidatively pretreatedactivated carbon as support, wherein the activated carbon has beennonoxidatively pretreated with water vapor, non-oxidizing mineral acidsor nonoxidizing organic acids or bases, and wherein the activated carbonhas not been oxidatively pre-treated.
 2. A catalyst as claimed in claim1, wherein the pretreatment of the activated carbon has been carried outusing HCl, H₃PO₄, formic acid, acetic acid, NH₄OH, NaOH of KOH.
 3. Aprocess for preparing ethers and lactones by catalytic hydrogenation ofcarboxylic acids, esters or anhydrides thereof, lactones or mixturesthereof over a catalyst comprising rhenium and platinum on activatedcarbon, wherein rhenium (calculated as metal) is used in a weight ratioto the activated carbon of from 0.0001 to 0.5, platinum (calculated asmetal) in a weight ratio to the activated carbon of from 0.0001 to 0.5and, optionally, at least on further metal selected from among Zn, Cu,Ag, Au, Ni, Fe, Ru, Mn, Cr, Mo, W and V in a weight ratio to theactivated carbon of from 0 to 0.25, wherein the activated carbon isnonoxidatively pretreated with nonoxidizing mineral acids ornonoxidizing organic acids or bases, the activated carbon is notoxidatively pretreated, and the hydrogenation is carried out at ahydrogen pressure of not more than 25 bar and a temperature in the rangeof from 180 to 235° C.